The present invention relates to signaling systems for communication between remote locations. The invention has particular application to remote control systems of the type which effects signaling over an AC power distribution circuit.
Conventionally, electrical appliance control within or around a building is achieved simply by the use of the existing power main together with switches at fixed locations and switches on the appliances. Remote control is not conventionally available other than by the use of switches at the fixed locations, or by local condition-responsive control of the switch on the appliance, such as, e.g., ultrasonic links directly to a television receiver, or timer-controlled automatic switches.
It is known to provide remote control of an appliance by signaling over the AC power lines, but such systems typically require access to both conductors of the AC power distribution circuit. Furthermore, most such systems require the generation of a separate modulated carrier signal to be impressed on the power line, such systems being disclosed, for example, in U.S. Pat. Nos. 4,200,862 and 4,300,126. It is also known to effect power line signaling by modulation of the AC power waveform itself, such a system being disclosed in U.S. Pat. No. 4,024,528. But that system also requires the generation of separate control signals to be superimposed on the AC voltage waveform. U.S. Pat. No. 4,292,546 teaches remote control of an appliance connected to the AC power line by momentary interruption of the AC power, which interruption is detected by a unit at the appliance to reverse the condition of its power switch. But such a system also momentarily interrupts power to any other device which may be connected to the AC circuit. This limits the utility of the system, since some AC-power devices would be adversely affected by such momentary power interruptions. Furthermore, 211 of these prior systems which effect signaling by some alteration of the AC power signal require access to both conductors of the AC line.